Which of my components has the better built in DAC?

My bet would be on the DA2module in your C2700.  But I would suggest that you listen to both and decide for yourself which you like best. As far as interconnects that’s subjective as well.  When I was using the DA1 in my MA8900 I used the usb connection so I can’t tell you which of the two options you mentioned is better.  Again you should try both and see which one you like.

The one that sounds better to YOU.

• USB:

  Offers the best potential for high-resolution audio transmission and is often considered the most versatile option. 

• Coaxial:

  A good choice for reliable digital signal transfer, especially if your DAC has a high-quality coaxial input. 

• Optical (Toslink):

  May be suitable for basic setups but may not support the highest sample rates compared to other options. 

There is no 'the best' DAC. There different chips and different output filters. Thus they all sound different. Pick the one you like. ESS chips tend to be brighter, AKM softer sounding, R2R - depends on manufacturer. Use USB.

My Dad has a MA8950 with the DA2 DAC and it really is a great sounding DAC module.   I think you would have to spend $$$ to better it.  It's that good.  

Coax is usually better than Tos because the quality of optical depends on the Tos jacks on the source and the DAC .    

If you read some threads on the DA2 card you'll see that people have spent a good amount on a DAC to find that it's splitting hairs.   

Plug the Node in via a good Coax and you're off to a good start.  Enjoy